From 27d673fbbb79b1b829484ec127da59b45f623ebd Mon Sep 17 00:00:00 2001
From: Kirk McKusick <mckusick@FreeBSD.org>
Date: Tue, 27 Sep 2022 08:57:30 -0700
Subject: [PATCH] When taking a snapshot on a UFS/FFS filesystem, it must be
 mounted.

The "update" mount option must be specified when the "snapshot"
mount option is used. Return EINVAL if the "snapshot" option is
specified without the "update" option also requested.

Reported by:  Robert Morris
Reviewed by:  kib
PR:           265362
MFC after:    2 weeks
Sponsored by: The FreeBSD Foundation
---
 sys/ufs/ffs/ffs_vfsops.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/sys/ufs/ffs/ffs_vfsops.c b/sys/ufs/ffs/ffs_vfsops.c
index 4768d610b28..8f6e186b44b 100644
--- a/sys/ufs/ffs/ffs_vfsops.c
+++ b/sys/ufs/ffs/ffs_vfsops.c
@@ -413,8 +413,11 @@ ffs_mount(struct mount *mp)
 	/*
 	 * If this is a snapshot request, take the snapshot.
 	 */
-	if (mp->mnt_flag & MNT_SNAPSHOT)
+	if (mp->mnt_flag & MNT_SNAPSHOT) {
+		if ((mp->mnt_flag & MNT_UPDATE) == 0)
+			return (EINVAL);
 		return (ffs_snapshot(mp, fspec));
+	}
 
 	/*
 	 * Must not call namei() while owning busy ref.